To tame C++ compile times, we should try to reduce the number of heavy dependencies in our .h files.
Two possible avenues come to mind:
- avoid including `unordered_map` and friends
- avoid including C++ stream libraries (such as `iostream`, `ios`, `sstream`...)
Unfortunately we're currently including `sstream` in `status.h` for some template APIs. We may move those to a separate include file (e.g. `status-builder.h`).